Revert of Don't handle NaturalScroll in Chrome but pass it to CMT instead

chrome/browser/chromeos/system/input_device_settings.h

Index: chrome/browser/chromeos/system/input_device_settings.h
diff --git a/chrome/browser/chromeos/system/input_device_settings.h b/chrome/browser/chromeos/system/input_device_settings.h
index ba938a13d1256af7700ec17edbc673a0c03a56de..901106af359965670d3843c67ac7444b2287a1b2 100644
--- a/chrome/browser/chromeos/system/input_device_settings.h
+++ b/chrome/browser/chromeos/system/input_device_settings.h
@@ -96,9 +96,6 @@
   void SetTapDragging(bool enabled);
   bool GetTapDragging() const;
 
-  void SetNaturalScroll(bool enabled);
-  bool GetNaturalScroll() const;
-
   // Updates |this| with |settings|. If at least one setting was updated returns
   // true.
   // |argv| is filled with arguments of script, that should be launched in order
@@ -110,7 +107,6 @@
   internal::Optional<bool> tap_to_click_;
   internal::Optional<bool> three_finger_click_;
   internal::Optional<bool> tap_dragging_;
-  internal::Optional<bool> natural_scroll_;
 };
 
 // Auxiliary class used to update several mouse settings at a time. User
@@ -177,9 +173,6 @@
   // Turns tap-dragging on/off.
   virtual void SetTapDragging(bool enabled) = 0;
 
-  // Turns natural scrolling on/off for all devices except wheel mice
-  virtual void SetNaturalScroll(bool enabled) = 0;
-
   // Calls |callback| asynchronously after determining if a mouse is connected.
   virtual void MouseExists(const DeviceExistsCallback& callback) = 0;